UV curable ferromagnetic compositions

ABSTRACT

The present invention discloses an ultraviolet light curable ferromagnetic composition and method for making such a composition that may be used to produce a ferromagnetic coating on a suitable substrate. These coatings may be used to produce printed capacitors and inductors. The disclosed composition does not contain any significant amount of volatile organic solvents that do not become incorporated in the active layer after curing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of International ApplicationSer. No. PCT/US01/00978, filed Jan. 11, 2001, that designates the UnitedStates of America and was published under PCT Article 21(2) in English,which, in turn, claims the benefit of U.S. provisional patentapplication Ser. No. 60/175,973, filed Jan. 13, 2000.

TECHNICAL FIELD

The present invention relates to ultraviolet light (uv) curablecompositions capable of producing a ferromagnetic coating.

BACKGROUND OF THE INVENTION

Electronic components, such as capacitors and inductors, are typicallyapplied to rigid circuit boards through the process of soldering.Electronic components may be produced applying curable compositions to asuitable substrate. Such film coatings have previously been formedthrough thermosetting and heat curing processes. Ferromagnetic materialsare materials which can be permanently magnetized upon application of anexternal magnetic field. Ferromagnetic coatings in particular, as usefulfor forming such electronic components as inductors and capacitors.

Heat curable coatings require the use of organic solvents that contain asignificant amount of volatile organic compounds (VOCs). These VOCsescape into the atmosphere while the heat curable coating dries. Suchsolvent based systems are undesirable because of the hazards andexpenses associated with VOCs. The hazards include water and airpollution and the expenses include the cost of complying with strictgovernment regulation on solvent emission levels. In contrast, UVcurable ferromagnetic film coatings contain reactive monomers instead ofsolvents; thus eliminating the detrimental effects of the VOCs.

UV curable coatings are cured through rapid photo-inducedpolymerizations instead of thermal energy which releases VOCs into theatmosphere. Since the UV curing process is essentially solvent free, thenecessity for time consuming and expensive pollution abatementprocedures is greatly reduced.

UV curable coatings offer several other benefits not associated withthermally cured coatings. First, faster cure times offer substantialeconomic benefits. Furthermore, heat sensitive materials can be safelycoated and cured with UV light without thermal degradation of heatsensitive substrates. Additionally, UV light is a relatively low cost ofenergy due to its widespread availability.

Although UV curable coatings are superior to their thermal counterparts,there are still disadvantages inherent in UV curable coatings. Since UVcurable coatings require compositions with high molecular weight andviscosity, spray and brush application is often difficult. Additionally,many UV curable coatings require compositions that are prone todispersion and instability.

Accordingly, there exists a need to provide environmentally safe UVcurable ferromagnetic compositions which exhibit improved performanceand workability. Additionally, there is a need to provide a method ofapplying an improved composition which furthers the goal of improvedperformance.

SUMMARY OF INVENTION

It is an object of the present invention to provide an improvedcomposition that upon curing by ultraviolet light produces aferromagnetic coating.

It is another object of the present invention to provide an improvedferromagnetic composition suitable for producing screen printedcapacitors and inductors.

It is another object of the present invention to provide an improvedferromagnetic composition suitable for coating a suitable substrate thatcan be applied by spraying, screen printing, dipping, and brushing.

It is still another object of the present invention to provide animproved ferromagnetic composition that does not contain any significantamount of volatile organic solvents that do not become incorporated inthe active layer after curing.

The present invention discloses an ultraviolet light curableferromagnetic composition and method for making such a composition thatmay be used to produce a ferromagnetic coating on a suitable substrate.The disclosed composition does not contain any significant amount ofvolatile organic solvents that do not become incorporated in the activelayer after curing. Specifically, the ferromagnetic composition contains5% or less volatile organic solvents by weight.

In accordance with one aspect of the invention, an ultraviolet lightcurable ferromagnetic composition is provided. The ferromagneticcomposition comprises a mixture of one or more aliphatic acrylatedoligomers, a magnetic powder, and a photoinitiator. Preferably, thealiphatic acrylated oligomer mixture is present in an amount of about15% to 45% of the total weight of the ferromagnetic composition, thephotoinitiator is present in an amount of about 1% to 10% of the totalweight of the ferromagnetic composition, and the magnetic powder ispresent in an amount of 20% to 60% of the total weight of theferromagnetic composition. All percentages of the ferromagneticcomposition as expressed in this document refer to the weight percentageof the stated component to the total weight of the ferromagneticcomposition in its fluid state at standard temperature and pressure.

The ferromagnetic composition preferably further comprises an acrylatedepoxy oligomer preferably present in an amount of about 2% to 6% of thetotal weight of the ferromagnetic composition and an unsaturated monomerpreferably present in an amount of about 15% to 25% of the total weightof the ferromagnetic composition. The ferromagnetic composition mayoptionally include a flow promoting agent preferably in an amount ofabout 0.1% to 6% of the ferromagnetic composition.

In accordance with yet another aspect of the invention, a method isprovided for depositing a ferromagnetic coating on a substrate. Themethod comprises a first step of applying to the substrate aferromagnetic fluid-phase composition (“ferromagnetic composition”). Theferromagnetic composition comprises a mixture of one or more aliphaticacrylated oligomers, a magnetic powder, and a photoinitiator.Preferably, the aliphatic acrylated oligomer mixture is present in anamount of about 15% to 45% of the total weight of the ferromagneticcomposition, the photoinitiator is present in an amount of about 1% to10% of the total weight of the ferromagnetic composition, and themagnetic powder is present in an amount of 20% to 60% of the totalweight of the ferromagnetic composition. The ferromagnetic compositionpreferably also includes an acrylated epoxy oligomer preferably presentin an amount of about 2% to 6% of the total weight of the ferromagneticcomposition, an unsaturated monomer preferably present in an amount ofabout 15% to 25% of the total weight of the ferromagnetic composition,and a flow promoting agent in an amount of about 0.1% to 6% of the totalweight of the ferromagnetic composition.

The method also includes a second step of illuminating the ferromagneticcomposition on the substrate with an ultraviolet light to cause theferromagnetic composition to cure into the ferromagnetic coating.

In accordance with this method, the ferromagnetic composition can beselectively deposited on the substrate at specific locations whereferromagnetic plating is desired. It need not be applied to the entiresubstrate.

BEST MODE FOR CARRYING OUT THE INVENTION

Ferromagnetic Compositions

Reference will now be made in detail to presently preferred compositionsor embodiments and methods of the invention, which constitute the bestmodes of practicing the invention presently known to the inventor.

In accordance with one aspect of the invention, a presently preferredultraviolet light curable ferromagnetic composition (“ferromagneticcomposition”) is provided. In this preferred embodiment, theferromagnetic composition includes a mixture of one or more aliphaticacrylated oligomers. The aliphatic acrylated oligomer mixture is presentin an amount of about 15% to 45% of the total weight of theferromagnetic composition. The aliphatic acrylated oligomer mixture ismore preferably present in an amount of about 25% to 35% of the totalweight of the ferromagnetic composition, and most preferably about 30%of the total weight of the ferromagnetic composition. The aliphaticacrylated oligomer preferably comprises one or more urethane oligomers.Suitable aliphatic acrylated oligomers include Radcure Ebecryl 244(aliphatic urethane diacrylate diluted 10% by weight with 1,6-hexanedioldiacrylate), Ebecryl 264 (aliphatic urethane triacrylate diluted 15% byweight with 1,6-hexanediol diacrylate), Ebecryl 284 (aliphatic urethanediacrylate diluted 12% by weight with 1,6-hexanediol diacrylate)urethanes, commercially available from Radcure UCB Corp. of Smyrna, Ga.;Sartomer CN-961E75 (aliphatic urethane diacrylate blended with 25% byweight ethoxylated trimethylol propane triacylate), CN-961H81 (aliphaticurethane diacrylate blended with 19% by weight 2(2-ethoxyethoxy)ethylacrylate), CN-963A80 (aliphatic urethane diacrylate blended with 20% byweight tripropylene glycol diacrylate), CN-964 (aliphatic urethanediacrylate), CN-966A80 (aliphatic urethane diacrylate blended with 20%by weight tripropylene glycol diacrylate), CN-982A75 (aliphatic urethanediacrylate blended with 25% by weight tripropylene glycol diacrylate)and CN-983 (aliphatic urethane diacrylate), commercially available fromSartomer Corp. of Exton, Pa.; TAB FAIRAD 8010, 8179, 8205, 8210, 8216,8264, M-E-15, UVU-316, commercially available from TAB Chemicals ofChicago, Ill.; and Echo Resin ALU-303, commercially available from EchoResins of Versaille, Mo.; and Genomer 4652, commercially available fromRahn Radiation Curing of Aurora, Ill. The preferred aliphatic acrylatedoligomers include Ebecryl 264 and Ebecryl 284. Ebecryl 264 is analiphatic urethane triacrylate of 1200 molecular weight supplied as an85% solution in hexanediol diacrylate. Ebecryl 284 is aliphatic urethanediacrylate of 1200 molecular weight diluted 10% with 1,6-hexanedioldiacrylate. Combinations of these materials may also be employed herein.

The preferred ferromagnetic composition still further includes amagnetic powder preferably in an amount of about 20% to 60% of the totalweight of the ferromagnetic composition. In one embodiment of thepresent invention, the magnetic powder will also possess high electricalconductivity Such powders, include, but are not limited to magnetizedsteel or iron ground into a powder. In a more preferred embodiment, themagnetic powder is a ferrite. In this particularly preferred embodiment,the magnetic powder will have a high resistivity. Because of thepresence of at least some electrical conductivity (whether low or highresistivity) the magnetic powder is sometimes referred to as aconductive/magnetic powder. The magnetic powder is more preferablypresent in an amount of about 30% to 50% of the total weight of theferromagnetic composition, and most preferably about 40% of the totalweight of the ferromagnetic composition. The preferred magnetic powderis Ferrite powder commercially available from GFS Chemical located inPowell, Ohio. Ferrites are magnetic substances that consist essentiallyof ferric oxide combined with the oxides of one or more metals (as iron,manganese, nickel, or zinc). Ferrites are described by MOFe₂O₃ whereFe₂O₃ is iron oxide and MO refers to a divalent metal (i.e, iron, zinc,nickel, manganese and copper) oxide.

The preferred ferromagnetic composition also includes a photoinitiatorin an amount of about 1% to 10% of the total weight of the ferromagneticcomposition of the ferromagnetic composition. The photoinitiator is morepreferably present in an amount of about 2% to 6% of the total weight ofthe ferromagnetic composition, and most preferably about 4.5% of thetotal weight of the ferromagnetic composition. Suitable photoinitiatorsinclude Irgacure 184 (1-hydroxycyclohexyl phenyl ketone), Irgacure 907(2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), Irgacure369 (2-benzyl-2-N,N-dimethylamino-1-(4-(4-morpholinophenyl)-1-butanone),Irgacure 500 (the combination of 50% by weight 1-hydroxy cyclohexylphenyl ketone and 50% by weight benzophenone), Irgacure 651(2,2-dimethoxy-2-phenyl acetophenone), Irgacure 1700 (the combination of25% by weight bis(2,6-dimethoxybenzoyl-2,4-,4-trimethyl pentyl)phosphine oxide, and 75% by weight2-hydroxy-2-methyl-1-phenyl-propan-1-one), Darocur 1173(2-hydroxy-2-methyl-1phenyl-1-propane) and Darocur 4265 (the combinationof 50% by weight 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide, and 50%by weight 2-hydroxy 2-methyl-1-phenyl-propan-1-one), availablecommercially from Ciba-Geigy Corp., Tarrytown, N.Y.; CYRACURE UVI-6974(mixed triaryl sulfonium hexafluoroantimonate salts) and CYRACUREUVI-6990 (mixed triaryl sulfonium hexafluorophosphate salts) availablecommercially from Union Carbide Chemicals and Plastics Co. Inc.,Danbury, Conn.; and Genocure CQ, Genocure BOK, and Genocure M.F.,commercially available from Rahn Radiation Curing. The preferredphotoinitiator is Irgacure 1700 commercially available from Ciba-Geigyof Tarrytown, N.Y. Combinations of these materials may also be employedherein.

This preferred ferromagnetic composition further includes an acrylatedepoxy oligomer. The acrylated epoxy oligomer is present in an amount ofabout 2% to 6% of the total weight of the ferromagnetic composition. Theacrylated epoxy oligomer is more preferably present in an amount ofabout 3% to 5% of the total weight of the ferromagnetic composition, andmost preferably about 4% of the total weight of the ferromagneticcomposition. Suitable acrylated epoxy oligomers include Radcure Ebecryl3603 (novolac epoxy acrylate diluted 20% by weight with tripropyleneglycol diacrylate), commercially available from Radcure UCB Corp.;Sartomer CN-120 (difunctional bisphenol based epoxy acrylate) and CN-124(difunctional bisphenol based epoxy acrylate), commercially availablefrom Sartomer Corp.; and Echo Resin TME 9310 and 9345, commerciallyavailable from Echo Resins. The preferred acrylated epoxy oligomer isEbecryl 3603, which is a tri-functional acrylated epoxy novolac.Combinations of these materials may also be employed herein.

The ferromagnetic composition preferably includes an ethylenicallyunsaturated monomer having Formula I:

wherein R₁ is hydrogen or substituted or unsubstituted alkyl; and R₂ issubstituted or unsubstituted alkyl having more than 4 carbon atoms,cycloalkyl, cycloalkenyl, or substituted or unsubstituted aryl.Preferably R₁ is hydrogen or methyl; and R₂ is isoborynl, phenyl,benzyl, dicylcopentenyl, diclypentenyl oxyethyl, cyclohexyl, andnaphthyl. The most preferred ethyleneically unsaturated monomers areisobornyl acrylate monomers. The isobornyl acrylate monomers arepreferably present in an amount of about 15% to 25% of the total weightof the ferromagnetic composition. The isobornyl acrylate monomer is morepreferably present in an amount of about 18% to 22% of the total weightof the ferromagnetic composition, and most preferably about 20% of thetotal weight of the ferromagnetic composition. Suitable isobornylacrylate monomers include Sartomer SR-423 (isobornyl methacrylate):

and SR-506 (isobornyl acrylate):

available from Sartomer Corp.; Radcure IBOA (isobornyl acrylate),commercially available from Radcure Corp.; IBOA and IBOMA, commerciallyavailable from CPS Chemical of Bradford, England; and Genomer 1121,commercially available from Rahn Radiation Curing. The preferredisobornyl acrylate monomer is Radcure IBOA, commercially available fromRadcure Corp. Radcure IBOA is a high purity, low color monomer.Combinations of these materials may also be employed herein.

The preferred ferromagnetic composition still further includes a flowpromoting agent in an amount of about 0.1% to 6% of the total weight ofthe ferromagnetic composition, and preferably about 3% of the totalweight of the ferromagnetic composition, of the paint composition.Suitable flow promoting agents include Genorad 17, commerciallyavailable from Rahn Radiation Curing; and Modaflow, commerciallyavailable from Monsanto Chemical Co., St. Louis, Miss. The preferredflow promoting agent is Modaflow which is an ethyl acrylate and2-ethylhexyl acrylate copolymer that improves the flow of thecomposition. Combinations of these materials may also be employedherein.

To illustrate, the following example sets forth a presently preferredferromagnetic composition according to this aspect of the invention.

EXAMPLE 1

This example provides a preferred ferromagnetic composition according tothe invention that may be applied to a substrate by screen printing. Theferromagnetic composition was made from the following components:

Approximate Component Weight % Ebecryl 264 15.1 Ebecryl 284 15.1 IBOA19.9 Irgacure 1700 4.5 Ebecryl 3603 4.0 Modaflow 2.9 Ferrite 38.5 Total100.00

In this example the IBOA and Irgacure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm. Inthe next step, the Ebecryl 264, the Ebecryl 284, the Ebecryl 3603, andModaflow are introduced into the pan and mixed for 1 to 2 minutes at aspeed of 2000 rpm. In the final step, the Ferrite is added and mixed at2000 rpm for 1 to 2 minutes. The mixing is temporarily suspended if thetemperature exceed 100° F.

Method for Depositing a Ferromagnetic Coating

In accordance with still another aspect of the invention, a method isprovided for depositing an ferromagnetic coating on a suitablesubstrate. The method comprises a first step of applying a ferromagneticfluid-phase composition (“ferromagnetic composition”) to the substrate.

The ferromagnetic composition comprises a mixture of one or morealiphatic acrylated oligomers, wherein the aliphatic acrylated oligomeris present in an amount of about 15% to 45% of the total weight of theferromagnetic composition. The ferromagnetic composition also includes amagnetic powder in an amount of about 20% to 60% of the total weight ofthe ferromagnetic composition, and a photoinitiator in an amount ofabout 1% to 10% of the total weight of the ferromagnetic composition.The ferromagnetic composition preferably includes an acrylated epoxyoligomer in an amount of about 2% to 6% of the total weight of theferromagnetic composition, an isobornyl acrylate monomer in an amount ofabout 15% to 25% of the total weight of the ferromagnetic composition,and a flow promoting agent in an amount of about 0.1% to 6% of the totalweight of the ferromagnetic composition. The preferred ferromagneticcompositions according to this method are those described herein, forexample, including the compositions described in example 1.

The ferromagnetic composition may be applied to the substrate using anumber of different techniques. The ferromagnetic composition may beapplied, for example, by direct brush application, or it may be sprayedonto the substrate surface. It also may be applied using a screenprinting technique. In such screen printing technique, a “screen” as theterm is used in the screen printing industry is used to regulate theflow of liquid composition onto the substrate surface. The ferromagneticcomposition typically would be applied to the screen as the lattercontacts the substrate. The ferromagnetic composition flows through thesilk screen to the substrate, whereupon it adheres to the substrate atthe desired film thickness. Screen printing techniques suitable for thispurpose include known techniques, but wherein the process is adjusted inways known to persons of ordinary skill in the art to accommodate theviscosity, flowability, and other properties of the liquid-phasecomposition, the substrate and its surface properties, etc. Flexographictechniques, for example, using pinch rollers to contact theferromagnetic composition with a rolling substrate, also may be used.

The method includes a second step of illuminating the ferromagneticfluid-phase composition on the substrate with an ultraviolet light tocause the ferromagnetic fluid-phase composition to cure into theferromagnetic coating. This illumination may be carried out in anynumber of ways, provided the ultraviolet light or radiation impingesupon the ferromagnetic composition so that the ferromagnetic compositionis caused to polymerize to form the coating, layer, film, etc., andthereby cures.

Curing preferably takes place by free radical polymerization, which isinitiated by an ultraviolet radiation source. The photoinitiatorpreferably comprises a photoinitiator, as described above.

Various ultraviolet light sources may be used, depending on theapplication. Preferred ultraviolet radiation sources for a number ofapplications include known ultraviolet lighting equipment with energyintensity settings of, for example, 125 watts, 200 watts, and 300 wattsper square inch.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A photocurable ferromagnetic composition comprising: an acrylated epoxy oligomer present in an amount from 2% to 6% of the weight of the ferromagnetic composition; an isobornyl acrylate monomer present in an amount from 15% to 25% of the weight of the ferromagnetic composition; a photoinitiator present in an amount from 1% to 10% of the weight of the ferromagnetic composition; and a magnetic powder present in an amount from 20% to 60% of the weight of the ferromagnetic composition.
 2. The photocurable ferromagnetic composition of claim 1 wherein the magnetic powder is ferrite.
 3. The photocurable ferromagnetic composition of claim 1 further comprising an acrylated aliphatic oligomer mixture.
 4. The photocurable ferromagnetic composition of claim 3 wherein the acrylated aliphatic oligomer mixture is present in an amount from 15% to 45% of the weight of the ferromagnetic composition.
 5. The photocurable ferromagnetic composition of claim 3 further comprising a flow promoting agent.
 6. The photocurable ferromagnetic composition of claim 5 wherein the flow promoting agent is present in an amount from 0.1% to 6% of the weight of the ferromagnetic composition.
 7. The photocurable ferromagnetic composition of claim 5 wherein: the acrylated epoxy oligomer is present in an amount from 3% to 5% of the weight of the ferromagnetic composition; the isobornyl acrylate monomer is present in an amount from 18% to 22% of the weight of the ferromagnetic composition; the photoinitiator is present in an amount from 2% to 6% of the weight of the ferromagnetic composition; the acrylated aliphatic oligomer mixture is present in an amount from 25% to 35% of the weight of the ferromagnetic composition; the flow promoting agent is present in an amount from 0.1% to 6% of the weight of the ferromagnetic composition; and the magnetic powder is present in an amount from 30% to 50% of the weight of the ferromagnetic composition.
 8. The photocurable ferromagnetic composition of claim 5 wherein: the acrylated epoxy oligomer is present in an amount of 4% of the weight of the ferromagnetic composition; the isobornyl acrylate monomer is present in an amount of 20% of the weight of the ferromagnetic composition; the photoinitiator is present in an amount of 4.5% of the weight of the ferromagnetic composition; the acrylated aliphatic oligomer mixture is present in an amount of 30% of the weight of the ferromagnetic composition; the flow promoting agent is present in an amount of 3% of the weight of the ferromagnetic composition; and the magnetic powder is present in an amount of 40% of the weight of the ferromagnetic composition.
 9. The ferromagnetic composition of claim 1 wherein the isobornyl acrylate monomer is selected from the group consisting of isobornyl acrylate, isobornyl methacrylate, and mixtures thereof.
 10. The ferromagnetic composition of claim 1 wherein the photoinitiator is selected from the group consisting of: 1-hydroxycyclohexyl phenyl ketone; 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-; the combination of 50% 1-hydroxy cyclohexyl phenyl ketone and 50% benzophenone; 2,2-dimethoxy-1,2-diphenylethan-1-one; the combination of 25% bis(2,6-dimethoxybenzoyl-2,4-, 4-trimethyl pentyl phosphine oxide and 75% 2-hydroxy-2-methyl-1-phenyl-propan-1-one; 2-hydroxy-2-methyl-1-phenyl-1-propane; the combination of 50% 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and 50% 2-hydroxy 2-methyl-1-phenyl-propan-1-one; mixed triaryl sulfonium hexafluoroantimonate salts, mixed triaryl sulfonium hexafluorophosphate salts; and mixtures thereof.
 11. The ferromagnetic composition of claim 1 wherein the acrylated epoxy oligomer is selected from the group consisting of: novolac epoxy acrylate diluted 20% by weight with tripropylene glycol diacrylate; difunctional bisphenol based epoxy acrylate; and mixtures thereof.
 12. A method for coating a substrate with a photocurable ferromagnetic composition, the method comprising: applying the ferromagnetic composition to the substrate, wherein the ferromagnetic composition includes: an acrylated epoxy oligomer present in an amount from 2% to 6% of the weight of the ferromagnetic composition; an isobornyl acrylate monomer present in an amount from 15% to 25% of the weight of the ferromagnetic composition; a photoinitiator present in an amount from 1% to 10% of the weight of the ferromagnetic composition; an acrylated aliphatic oligomer mixture present in an amount from 15% to 45% of the weight of the ferromagnetic composition; a flow promoting agent present in an amount from 0.1% to 6% of the weight of the ferromagnetic composition; and a magnetic powder present in an amount from 20% to 60% of the weight of the ferromagnetic composition.
 13. The method of claim 12, wherein UV light used in illuminating impinges upon the ferromagnetic composition so that the ferromagnetic composition is caused to form a coating as it cures.
 14. The method of claim 12, wherein the method of applying the ferromagnetic composition is spraying.
 15. The method of claim 12, wherein the method of applying the ferromagnetic composition is screen printing.
 16. The method of claim 12, wherein the method of applying the ferromagnetic composition is dipping the substrate into the composition sufficiently to cause the composition to uniformly coat the substrate.
 17. The method of claim 12, wherein the method of applying the ferromagnetic composition is brushing.
 18. The method of claim 12, wherein the method of applying the ferromagnetic composition is selectively depositing to the, substrate at predetermined locations.
 19. A method for coating a substrate with a photocurable ferromagnetic composition, the method comprising: applying the ferromagnetic composition to the substrate, wherein the ferromagnetic composition includes: an acrylated epoxy oligomer present in an amount from 3% to 5% of the weight of the ferromagnetic composition; an isobornyl acrylate monomer present in an amount from 18% to 22% of the weight of the ferromagnetic composition; a photoinitiator present in an amount from 2% to 6% of the weight of the ferromagnetic composition; an acrylated aliphatic oligomer mixture present in an amount from 25% to 35% of the weight of the ferromagnetic composition; a flow promoting agent present in an amount from 0.1% to 6% of the weight of the ferromagnetic composition; and a magnetic powder present in an amount from 30% to 50% of the weight of the ferromagnetic composition; illuminating the ferromagnetic composition with a UV light sufficient to cause the ferromagnetic composition to be incorporated into the ferromagnetic coating by the time the composition is cured.
 20. The method of claim 19, wherein: the acrylated epoxy oligomer is present in an amount of 4% of the weight of the ferromagnetic composition; the isobornyl acrylate monomer is present in an amount of 20% of the weight of the ferromagnetic composition; the photoinitiator is present in an amount of 4.5% of the weight of the ferromagnetic composition; the acrylated aliphatic oligomer mixture is present in an amount of 30% of the weight of the ferromagnetic composition; the flow promoting agent is present in an amount of 3% of the weight of the ferromagnetic composition; and the magnetic powder is present in an amount of 40% of the weight of the ferromagnetic composition.
 21. A method of making a photocurable ferromagnetic composition comprising: mixing from 15% to 25% by weight of isobornyl acrylate monomer and from 1% to 10% by weight of a photoinitiator in a pan: introducing from 0.1% to 6% by weight of a flow-promoting agent and from 2% to 6% by weight of an acrylated epoxy oligomer into the pen; mixing said flow-promoting agent and said epoxy acrylate oligomer in the pan; introducing from 20% to 60% by weight of a magnetic powder into the pan; and mixing the magnetic powder in the pan, wherein all weight percents are based on the weight of the ferromagnetic composition. 